1. Field of the Invention
Our invention falls within the field of non-destructive testing and more particularly falls within the area of non-destructive testing to ascertain thermal qualities of structures or materials. Our method is applicable to testing anisotropic layered structures by observing surface temperature changes during the course of a controlled heating of the surface.
2. Background Art
Various techniques are known and used to ascertain thermal properties of layered structures wherein heat is applied to the structure and temperature changes at the surface or an interface are observed. In these techniques experimental data is used, via modeling and optimization or error minimization processes to derive thermal properties such as thermal conductivity or thermal diffusivity. See, for example, a paper by Model in International Journal of Thermophysics, Vol. 26, No. 1, January 2003 titled “Thermal Transport Properties of Layered Materials: Identification by a New Numerical Algorithm for Transient Measurements.” That paper contemplates a mathematical model wherein a flat, planar heat source is sandwiched at the interface between two identical layered structures. The use of lowered surface heat excitation frequencies to elicit thermal responses of deeper zones within a structure was discussed in “Thermal Non-Destructive Characterization by the Thermal Transfer Function and the Numerical Method of Control Volumes” by Bellatar et al., at NDT.net August 2003, Vol. 8 No. 8.